A mobile radio network may include hundreds or possibly thousands of wireless terminals each of which requires updating with software or data files from time to time. Terminals are preferably updated over the air using a broadcast protocol, rather than being manually brought to a central site or visited individually at remote sites. The same or similar files can usually be transmitted to each terminal.
Private mobile radio (PMR) networks typically provide a relatively small number of broadcast channels each with relatively narrow bandwidth, compared to wired or spread spectrum systems for example. In many cases the networks are also unreliable or lossy in that signals to some or all of the wireless terminals are imperfectly received for various reasons. These terminals may then request multiple repeats of a particular transmission.
Files should therefore be transmitted on the downlink to the terminals as efficiently as possible and repeat transmissions of all or part of each file must be managed. Contention between the terminals on the uplink when acknowledging receipt of the files must also be efficiently managed.